CN113204114A - Display module and display device - Google Patents
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- CN113204114A CN113204114A CN202110118599.9A CN202110118599A CN113204114A CN 113204114 A CN113204114 A CN 113204114A CN 202110118599 A CN202110118599 A CN 202110118599A CN 113204114 A CN113204114 A CN 113204114A
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- 210000001747 pupil Anatomy 0.000 claims abstract description 13
- 230000003287 optical effect Effects 0.000 claims description 50
- 239000000463 material Substances 0.000 description 7
- 238000002834 transmittance Methods 0.000 description 7
- 230000005540 biological transmission Effects 0.000 description 5
- 230000002093 peripheral effect Effects 0.000 description 5
- 238000004088 simulation Methods 0.000 description 4
- 230000004075 alteration Effects 0.000 description 3
- 238000005286 illumination Methods 0.000 description 3
- 230000015572 biosynthetic process Effects 0.000 description 2
- 239000003086 colorant Substances 0.000 description 2
- 230000000694 effects Effects 0.000 description 2
- 210000003128 head Anatomy 0.000 description 2
- 239000002184 metal Substances 0.000 description 2
- 230000002146 bilateral effect Effects 0.000 description 1
- 238000010586 diagram Methods 0.000 description 1
- 239000006185 dispersion Substances 0.000 description 1
- 238000005401 electroluminescence Methods 0.000 description 1
- 239000011521 glass Substances 0.000 description 1
- 239000004973 liquid crystal related substance Substances 0.000 description 1
- 238000012986 modification Methods 0.000 description 1
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- G—PHYSICS
- G02—OPTICS
- G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
- G02B27/00—Optical systems or apparatus not provided for by any of the groups G02B1/00 - G02B26/00, G02B30/00
- G02B27/01—Head-up displays
- G02B27/017—Head mounted
- G02B27/0172—Head mounted characterised by optical features
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- G—PHYSICS
- G02—OPTICS
- G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
- G02B27/00—Optical systems or apparatus not provided for by any of the groups G02B1/00 - G02B26/00, G02B30/00
- G02B27/42—Diffraction optics, i.e. systems including a diffractive element being designed for providing a diffractive effect
- G02B27/4205—Diffraction optics, i.e. systems including a diffractive element being designed for providing a diffractive effect having a diffractive optical element [DOE] contributing to image formation, e.g. whereby modulation transfer function MTF or optical aberrations are relevant
- G02B27/4211—Diffraction optics, i.e. systems including a diffractive element being designed for providing a diffractive effect having a diffractive optical element [DOE] contributing to image formation, e.g. whereby modulation transfer function MTF or optical aberrations are relevant correcting chromatic aberrations
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- G—PHYSICS
- G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
- G03H—HOLOGRAPHIC PROCESSES OR APPARATUS
- G03H1/00—Holographic processes or apparatus using light, infrared or ultraviolet waves for obtaining holograms or for obtaining an image from them; Details peculiar thereto
- G03H1/02—Details of features involved during the holographic process; Replication of holograms without interference recording
- G03H1/024—Hologram nature or properties
- G03H1/0248—Volume holograms
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- G—PHYSICS
- G02—OPTICS
- G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
- G02B27/00—Optical systems or apparatus not provided for by any of the groups G02B1/00 - G02B26/00, G02B30/00
- G02B27/01—Head-up displays
- G02B27/0101—Head-up displays characterised by optical features
- G02B2027/011—Head-up displays characterised by optical features comprising device for correcting geometrical aberrations, distortion
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- G—PHYSICS
- G02—OPTICS
- G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
- G02B27/00—Optical systems or apparatus not provided for by any of the groups G02B1/00 - G02B26/00, G02B30/00
- G02B27/01—Head-up displays
- G02B27/0101—Head-up displays characterised by optical features
- G02B2027/0112—Head-up displays characterised by optical features comprising device for genereting colour display
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- G—PHYSICS
- G02—OPTICS
- G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
- G02B27/00—Optical systems or apparatus not provided for by any of the groups G02B1/00 - G02B26/00, G02B30/00
- G02B27/01—Head-up displays
- G02B27/017—Head mounted
- G02B27/0172—Head mounted characterised by optical features
- G02B2027/0174—Head mounted characterised by optical features holographic
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- G—PHYSICS
- G02—OPTICS
- G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
- G02B27/00—Optical systems or apparatus not provided for by any of the groups G02B1/00 - G02B26/00, G02B30/00
- G02B27/01—Head-up displays
- G02B27/017—Head mounted
- G02B2027/0178—Eyeglass type
Abstract
Display module and display device. The display module of the present invention has: an image light generation device that generates image light; a 1 st diffraction element having a 1 st surface and a 2 nd surface and diffracting image light; a 1 st reflecting part which reflects the image light; and a 2 nd diffraction element having a 3 rd surface and diffracting the image light, wherein the 1 st diffraction element transmits the image light incident on the 1 st surface from the image light generation device and emits the image light from the 2 nd surface to a 1 st reflection unit, the 1 st reflection unit reflects the image light emitted from the 1 st diffraction element toward the 2 nd surface of the 1 st diffraction element, the 1 st diffraction element diffracts the image light incident on the 2 nd surface from the 1 st reflection unit and emits the image light from the 2 nd surface to the 2 nd diffraction element, and the 2 nd diffraction element diffracts the image light incident on the 3 rd surface from the 1 st diffraction element and emits the image light from the 3 rd surface to form an exit pupil.
Description
Technical Field
The invention relates to a display module and a display device.
Background
There is known a head-mounted display device of a type in which a plurality of reflection surfaces reflect image light and guide the image light to the eyes of an observer. Patent document 1 discloses a head-mounted display device including: 1 st optical portion having positive refractive power: a 2 nd optical part having a 1 st diffraction element and having a positive refractive power; a 3 rd optical portion having a positive refractive power; and a 4 th optical part having a 2 nd diffraction element and having a positive refractive power. In this display device, a 1 st intermediate image of image light is formed between a 1 st optical portion and a 3 rd optical portion, a pupil is formed between a 2 nd optical portion and a 4 th optical portion, a 2 nd intermediate image of image light is formed between the 3 rd optical portion and the 4 th optical portion, and an exit pupil is formed on the side of the 4 th optical portion opposite to the 3 rd optical portion.
Patent document 1: japanese patent laid-open publication No. 2019-133132
In the display device of patent document 1, the optical members are arranged so that the positional relationship between the optical members satisfies a specific condition so as to compensate for chromatic dispersion by using two diffraction elements. Therefore, a large space is required for disposing the optical members, and the display device may be large.
Disclosure of Invention
In order to solve the above problem, a display module according to an embodiment of the present invention includes: an image light generation device that generates image light; a 1 st diffraction element having a 1 st surface and a 2 nd surface, which diffracts the image light; a 1 st reflecting section that reflects the image light; and a 2 nd diffraction element having a 3 rd surface for diffracting the image light, wherein the 1 st diffraction element transmits the image light incident on the 1 st surface from the image light generation device and emits the image light from the 2 nd surface to the 1 st reflection portion, the 1 st reflection portion reflects the image light emitted from the 1 st diffraction element toward the 2 nd surface of the 1 st diffraction element, the 1 st diffraction element diffracts the image light incident on the 2 nd surface from the 1 st reflection portion and emits the image light from the 2 nd surface to the 2 nd diffraction element, and the 2 nd diffraction element diffracts the image light incident on the 3 rd surface from the 1 st diffraction element and emits the image light from the 3 rd surface to form an emission pupil.
A display device according to one embodiment of the present invention includes: a display module according to one embodiment of the present invention; and a housing that houses the display module.
Drawings
Fig. 1 is a perspective view of a display device according to embodiment 1.
Fig. 2 is a plan view showing the structure of the display module according to embodiment 1.
Fig. 3 is a side view showing the structure of the display module of embodiment 1.
Fig. 4 is an explanatory view of interference fringes of the volume hologram element.
Fig. 5 is a graph showing diffraction characteristics of the 1 st diffraction element and the 2 nd diffraction element.
Fig. 6 is a graph showing the transmittance at the refractive index difference Δ n of 0.035 with respect to the wavelength in the 1 st diffraction element.
Fig. 7 is a graph showing the relationship of the transmittance at the refractive index difference Δ n of 0.019 with respect to the wavelength in the 1 st diffraction element.
Fig. 8 is a graph showing the relationship between the transmittance at the refractive index difference Δ n of 0.010 and the wavelength in the 1 st diffraction element.
Fig. 9 is a graph showing the relationship between the transmittance at which the refractive index difference Δ n is 0.005 and the wavelength in the 1 st diffraction element.
Fig. 10 is a plan view showing the structure of the display module according to embodiment 2.
Description of the reference symbols
10. 12: a display module; 10 a: a display module for the right eye; 10 b: a display module for the left eye; 20: an image light generating device; 30: a 1 st reflecting part; 50. 55: a 1 st diffraction element; 50a, 55 a: the 1 st surface; 50b, 55 b: the 2 nd surface; 55 h: a light transmitting section; 60: a 2 nd reflecting part; 70. 70a, 70 b: a 2 nd diffraction element; 70 c: the 3 rd surface; 90: a housing; 100: a display device; 502. 502B, 502G, 502R: interference fringes; 505: a low refractive index portion; 506: a high refractive index portion; l0, L0a, L0 b: image light; g: an exit pupil; k10, K20: a normal direction; k11: the 1 st direction; k22: and (2) a direction.
Detailed Description
[ embodiment 1 ]
Hereinafter, embodiment 1 of the present invention will be described with reference to fig. 1 to 9.
Fig. 1 is a perspective view showing a head-mounted display device according to the present embodiment. Fig. 2 is a plan view showing a schematic configuration of a display module of the head-mounted display device. Fig. 3 is a side view showing a schematic structure of the display module.
In the following description, the head-mounted display device is simply referred to as a display device. In the drawings below, the components may be shown in different scales depending on the components in order to facilitate the observation of the components.
In the following drawings, the following directions are defined using the front-back direction, the left-right direction, and the up-down direction in a state where the display device 100 is worn on the head by the observer. An axis along the vertical direction is defined as a Y axis, a direction from the lower side to the upper side is defined as a + Y direction, and a direction from the upper side to the lower side is defined as a-Y direction. An axis along the front-rear direction is a Z axis, a direction from the rear to the front is a + Z direction, and a direction from the front to the rear is a-Z direction. Let the axis along the left-right direction be the X axis, the direction from right to left be the + X direction, and the direction from left to right be the-X direction. The Y-axis, the Z-axis and the X-axis are perpendicular to each other.
When the above-described directions are defined using the components of the display device 100, an axis connecting the center of the 2 nd diffraction element 70a of the right-eye display module 10a and the center of the 2 nd diffraction element 70b of the left-eye display module 10b is defined as an X axis, a direction from the 2 nd diffraction element 70a toward the 2 nd diffraction element 70b is defined as a + X direction, and a direction from the 2 nd diffraction element 70b toward the 2 nd diffraction element 70a is defined as a-X direction. In the display module 10 described later, the optical axis of the exit pupil is defined as the Z axis, the direction from the exit pupil to the 2 nd diffraction element 70a or the 2 nd diffraction element 70b is defined as the + Z direction, and the direction from the 2 nd diffraction element 70a or the 2 nd diffraction element 70b to the exit pupil is defined as the-Z direction. Let an axis along a vertical direction of the display surface of the image light generating device 20 be a Y axis, a direction from below to above the display surface be a + Y direction, and a direction from above to below the display surface be a-Y direction.
As shown in fig. 1, the display device 100 includes: a right-eye display module 10a that causes image light L0a to enter the right eye Ea of the observer; a left-eye display module 10b for making the image light L0b incident on the left eye Eb of the observer; and a case 90 that houses the right-eye display module 10a and the left-eye display module 10 b. The display device 100 has a shape like glasses, for example. The display device 100 is worn on the head of the observer through the housing 90.
The housing 90 has: a frame 91; a temple 92a provided on the right side of the frame 91 and locked to the right ear of the observer; and a temple 92b provided on the left side of the frame 91 and locked to the left ear of the observer. The frame 91 has storage spaces 91s at both side portions, and various optical elements constituting the optical module 10 described later are stored in the storage spaces 91 s. The temples 92a, 92b are connected to the frame 91 via hinges 95 so as to be foldable.
The right-eye display module 10a and the left-eye display module 10b are different in that the optical members are arranged in bilateral symmetry, but have the same basic configuration. Therefore, in the following description, the configuration will be described as the display module 10 without distinguishing the right-eye display module 10a and the left-eye display module 10 b.
As shown in fig. 2 and 3, the display module 10 of the present embodiment includes an image light generating device 20, a condensing optical system 25, a 1 st diffraction element 50, a 1 st reflection unit 30, a 2 nd reflection unit 60, and a 2 nd diffraction element 70.
The image light generation device 20 generates image light L0. The condensing optical system 25 projects the image light L0 generated by the image light generation device 20. The 1 st diffraction element 50 has a 1 st surface 50a and a 2 nd surface 50b, and diffracts the image light L0. The 1 st reflection unit 30 reflects the image light L0. The 2 nd reflection unit 60 reflects the image light L0 diffracted by the 1 st diffraction element 50 toward the 2 nd diffraction element 70. The 2 nd diffraction element 70 has a 3 rd surface 70c, and diffracts the image light L0 to form an exit pupil G.
The image light generation device 20 is constituted by a display panel such as an organic electroluminescence display element. The image light generation device 20 is disposed rearward of the side of the eye E in a state where the display device 100 is worn by the observer, and emits the image light L0 forward. The image light generation device 20 is disposed such that the optical axis L01 of the image light L0 is substantially parallel to the Z axis.
The image light generation device 20 may include a plurality of display panels corresponding to mutually different colors, and a synthesis optical system for synthesizing image lights of the respective colors emitted from the plurality of display panels. The image light generation device 20 may include an illumination light source and a display panel such as a liquid crystal display element that modulates illumination light emitted from the illumination light source. Alternatively, the image light generation device 20 may be configured to modulate laser light using a micromirror device. Alternatively, the image light generation device 20 may be constituted by a Micro LED, a MEMS display, or the like.
The optical axis L01 of the image light L0 is an axis through which the central principal ray of the image light L0 emitted from the center of the display region of the image light generation device 20 passes. In other words, the optical axis L01 of the image light L0 is an axis passing through the center of the exit surface 20a of the image light generation device 20 and along the normal to the exit surface 20 a. In addition, in the case where the image light generation device 20 is configured by a laser light source and a mirror that scans light from the laser light source, since an image plane is formed by the scanning of the laser light, the optical axis of the image light L0 is an axis that passes through the center of the image plane and is parallel to the normal line of the image plane.
The condensing optical system 25 is an optical system that condenses the image light L0 generated by the image light generation device 20, and has a plurality of lenses. In the present embodiment, the condensing optical system 25 is configured by 4 lenses 251, 252, 253, and 254 provided along the optical axis L01 of the image light L0. However, the number of lenses constituting the condensing optical system 25 is not particularly limited. Further, as the lens, a structure in which a plurality of lenses are bonded, for example, a achromat is bonded may be used. The lens may be an aspherical lens such as a free-form surface lens or a spherical lens.
The 1 st diffraction element 50 has a reflection type volume hologram element. The 1 st diffraction element 50 includes: a 1 st surface 50a facing the condensing optical system 25; and a 2 nd surface 50b facing the 1 st reflecting portion 30. The 2 nd surface 50b of the 1 st diffraction element 50 on which the image light L0 enters from the 1 st reflection part 30 is a concave curved surface. In other words, the 2 nd surface 50b has a shape in which the central portion is concave and curved with respect to the peripheral portion in the incident direction of the image light L0 from the 1 st reflection portion 30. Accordingly, the 1 st diffraction element 50 has positive refractive power, and can efficiently deflect the image light L0 toward the 2 nd reflection unit 60.
The 1 st diffraction element 50 is a reflection type diffraction element, but 0 th order diffraction light is transmitted from the 1 st plane 50a to the 2 nd plane 50b by appropriately setting the refractive index of each of the low refractive index portion and the high refractive index portion constituting the interference fringe. The 1 st diffraction element 50 transmits the image light L0 emitted from the image light generating device 20 as 0 th order diffraction light from the 1 st plane 50a to the 2 nd plane 50b, and emits the image light L0 emitted from the 1 st reflection unit 30 as 1 st order diffraction light from the 2 nd plane 50b to the 2 nd diffraction element 70. As for the interference fringes, detailed description will be made later.
The 1 st diffraction element 50 is not limited to the volume hologram element as long as it is a reflection type diffraction element that can transmit the 0 th order diffracted light, and may be formed of, for example, a surface relief type diffraction element, a surface relief hologram element, or the like. The 1 st diffraction element 50 has a characteristic that when the image light L0 enters from the normal direction of the 2 nd surface 50b, diffracted light having the highest diffraction efficiency is emitted in a specific direction.
Fig. 4 is an explanatory diagram of interference fringes of the volume hologram element constituting the 1 st diffraction element 50.
As shown in fig. 4, interference fringes 502 are provided in the volume hologram element constituting the 1 st diffraction element 50, and the interference fringes 502 have a pitch corresponding to a specific wavelength. The interference fringe 502 has a structure in which low refractive index portions 505 having a relatively low refractive index and high refractive index portions 506 having a relatively high refractive index are alternately provided. Therefore, the interference fringes 502 are recorded in the photosensitive layer of the hologram element as a refractive index difference of the material constituting the hologram element.
The interference fringes 502 are inclined in one direction with respect to the 2 nd surface 50b of the 1 st diffraction element 50 so as to correspond to a specific incident angle. Thus, the 1 st diffraction element 50 diffracts the image light L0 in the predetermined direction so as to form a predetermined angle with respect to the normal direction of the 2 nd surface 50 b. The specific wavelength and the specific incident angle correspond to the wavelength and the incident angle of the image light L0. The interference fringes 502 can be formed by subjecting the hologram photosensitive layer to interference exposure using the reference light Lr and the object light Ls.
The image light L0 is light for color display including the red light LR, the green light LG, and the blue light LB. Therefore, in the 1 st diffraction element 50, interference fringes 502 are formed at a pitch corresponding to a specific wavelength. For example, the interference fringes 502R for red light are formed at a pitch corresponding to, for example, a wavelength 615nm in a wavelength range of 580nm to 700nm in the red wavelength band. The interference fringes 502G for green light are formed at a pitch corresponding to, for example, a wavelength 535nm in a wavelength range of 500nm to 580nm in the green wavelength band. The interference fringes 502B for blue light are formed at a pitch corresponding to, for example, a wavelength of 460nm in a wavelength range of 400nm to 500nm in the blue wavelength band.
In fig. 4, the interference fringes 502 are linearly drawn, but when the image light L0 incident on the 1 st diffraction element 50 is a spherical wave, for example, a spherical wave is used as the object light Ls in the interference exposure. In this case, a plurality of interference fringes 502 are formed in a curved state on each of the hologram photosensitive layers. Therefore, the interference fringes 502 are inclined in one direction with respect to the 2 nd surface 50b of the 1 st diffraction element 50 in a curved state. Thus, when the image light L0 formed of a spherical wave of a single wavelength is incident from the normal direction of the 2 nd surface 50b, the 1 st diffraction element 50 emits the diffracted light L1 having the highest diffraction efficiency in a specific direction inclined with respect to the normal direction. When the interference fringe 502 is curved, the inclination direction of the interference fringe 502 is defined as, for example, the inclination of a straight line connecting both ends of the interference fringe 502.
As shown in fig. 2 and 3, the 1 st reflecting part 30 is formed of a total reflection mirror. Specifically, the 1 st reflecting section 30 includes a base material, and a reflecting layer formed on one surface of the base material and composed of a dielectric multilayer film, a metal film, or the like. The 1 st reflecting part 30 is disposed such that a normal line V1 of the reflecting surface 30a is substantially parallel to the Z axis. The reflection surface 30a is formed of a free-form surface, and the 1 st reflection part 30 has positive refractive power.
The 2 nd reflecting part 60 is constituted by a total reflection mirror. Specifically, the 2 nd reflecting portion 60 includes a base material, and a reflecting layer formed on one surface of the base material and composed of a dielectric multilayer film, a metal film, or the like. The 2 nd reflecting portion 60 is disposed to be inclined in a direction in which the angle formed by the normal line V2 of the reflecting surface 60a and the Z axis is substantially 45 °. The reflecting surface 60a is formed of a curved surface, and the 2 nd reflecting portion 60 has positive refractive power.
The 2 nd diffraction element 70 has a volume hologram element of a reflection type. The 2 nd diffraction element 70 has a 3 rd surface 70c facing the eye E of the observer and a 4 th surface 70d different from the 3 rd surface. The 3 rd surface 70c of the 2 nd diffraction element 70 on which the image light L0 is incident is a concave curved surface. In other words, the 3 rd surface 70c has a shape in which the central portion is recessed and curved with respect to the peripheral portion in the incident direction of the image light L0. Thus, the 2 nd diffraction element 70 has positive refractive power, and can efficiently deflect the image light L0 toward the exit pupil G. The 2 nd diffraction element 70 is arranged to be inclined so that an end portion 70e on a side close to the nose of the observer is located in the-Z direction with respect to an end portion 70f on a side far from the nose.
The basic structure of the volume hologram element constituting the 2 nd diffraction element 70 is the same as that of the volume hologram element constituting the 1 st diffraction element 50, and therefore, detailed description of the volume hologram element is omitted. However, the volume hologram element constituting the 2 nd diffraction element 70 is constituted by a partial reflection type diffraction optical element that reflects a part of incident light and transmits the other part. Therefore, the 2 nd diffraction element 70 functions as a combiner of partial transmission/reflection properties. Thus, since the external light is incident on the eye E of the observer via the 2 nd diffraction element 70, the observer can see an image in which the image formed by the image light generation device 20 is superimposed on the background.
The 2 nd diffraction element 70 is not limited to the volume hologram element as long as it is a reflection type diffraction element, and may be, for example, a surface relief type diffraction element, a surface relief hologram element, or the like. The 2 nd diffraction element 70 has a characteristic that diffracted light having the highest diffraction efficiency is emitted in a specific direction when the image light L0 enters from the normal direction of the 3 rd surface 70c, regardless of the configuration.
Fig. 5 is a graph showing diffraction characteristics of the 1 st diffraction element 50 and the 2 nd diffraction element 70.
Fig. 5 shows the difference in diffraction angle between a specific wavelength and a peripheral wavelength when a light ray is incident on 1 point on the volume hologram element. In FIG. 5, when the specific wavelength is 531nm, the solid line L526 shows the deviation of the diffraction angle of the light having the peripheral wavelength of 526nm, and the broken line L536 shows the deviation of the diffraction angle of the light having the peripheral wavelength of 536 nm.
As shown in fig. 5, even in the case where light is incident on the same interference fringes recorded by the volume hologram element, the longer the wavelength of the light, the larger the angle of diffraction, and the shorter the wavelength of the light, the smaller the angle of diffraction. Therefore, when 2 diffraction elements including the 1 st diffraction element 50 and the 2 nd diffraction element 70 are used, it is not possible to appropriately compensate for the aberration when the light having the long wavelength and the light having the short wavelength are incident without considering the incident angle with respect to the specific wavelength. Since the diffraction angle varies depending on the number of interference fringes, the structure of the interference fringes needs to be considered. In the display module 10 of the present embodiment shown in fig. 2, the orientations of the 1 st diffraction element 50 and the 2 nd diffraction element 70 with respect to the image light L0 and the like are optimized according to whether the sum of the number of formation times and the number of reflection times of the intermediate image between the 1 st diffraction element 50 and the 2 nd diffraction element 70 is an odd number or an even number, and therefore, aberrations can be compensated for.
Here, an imaginary plane including a normal line V3 of the 2 nd surface 50b of the 1 st diffraction element 50 and a normal line V4 of the 3 rd surface 70c of the 2 nd diffraction element 70 is assumed. In the present embodiment, the imaginary plane is the plane of fig. 2, that is, the XZ plane.
In the present embodiment, the sum of the number of reflections of the image light L0 between the 1 st diffraction element 50 and the 2 nd diffraction element 70 and the number of generation of the intermediate image is an even number. Therefore, when light enters from the normal direction of the 2 nd surface 50b or the 3 rd surface 70c when viewed from the normal direction of the virtual surface, the directions of diffracted light emitted with the highest diffraction efficiency of the 1 st diffraction element 50 and the 2 nd diffraction element 70 are set on the same side with respect to the normal direction of the 2 nd surface 50b or the 3 rd surface 70 c.
More specifically, in the present embodiment, since the 2 nd reflection unit 60 is provided on the optical path of the image light L0 between the 1 st diffraction element 50 and the 2 nd diffraction element 70, the image light L0 is reflected 1 time between the 1 st diffraction element 50 and the 2 nd diffraction element 70. Further, the 1 st diffraction element 50, the 1 st reflection part 30, and the 2 nd reflection part 60 each have positive refractive power, and 1 intermediate image Z1 is generated between the 2 nd reflection part 60 and the 2 nd diffraction element 70. Therefore, the sum of the number of reflections of the image light L0 between the 1 st diffraction element 50 and the 2 nd diffraction element 70 and the number of generation of the intermediate image is 2, that is, an even number.
Therefore, the 1 st diffraction element 50 and the 2 nd diffraction element 70 are disposed such that the 1 st direction with respect to the normal direction of the 2 nd surface 50b and the 2 nd direction with respect to the normal direction of the 3 rd surface 70c are on the same side as the 2 nd direction with respect to the normal direction of the 2 nd surface 50b, provided that the direction in which the image light L0 is emitted with the highest diffraction efficiency when the image light L0 is incident from the normal direction of the 2 nd surface 50b is the 1 st direction, and the direction in which the image light L0 is emitted with the highest diffraction efficiency when the image light L0 is incident from the normal direction of the 3 rd surface 70c is the 2 nd direction.
More specifically, as shown in fig. 2, when light enters the 2 nd surface 50b of the 1 st diffraction element 50 from the normal direction K10, the 1 st direction K11 in which diffracted light having the highest diffraction efficiency is emitted is positioned after being rotated clockwise CW with respect to the normal direction K10 of the 2 nd surface 50 b. When light enters the 3 rd surface 70c of the 2 nd diffraction element 70 from the normal direction K20, the 2 nd direction K22 from which diffracted light having the highest diffraction efficiency is emitted is positioned after being rotated in the clockwise direction CW with reference to the normal direction K20 of the 3 rd surface 70 c.
That is, the 1 st direction K11 in which the 1 st diffraction element 50 emits the diffracted light with the highest diffraction efficiency and the 2 nd direction K22 in which the 2 nd diffraction element 70 emits the diffracted light with the highest diffraction efficiency are located on the same side with respect to the normal direction K10 of the 2 nd surface 50b or the normal direction K20 of the 3 rd surface 70 c. This structure is realized by associating the inclination direction of the interference fringes of the 1 st diffraction element 50 with the inclination direction of the interference fringes of the 2 nd diffraction element 70.
According to this configuration, when the light beam having the optimum wavelength is incident from the normal direction K10 of the 2 nd surface 50b of the 1 st diffraction element 50, the diffracted light when the light beam having the wavelength longer than the optimum wavelength is incident is inclined in the clockwise direction. Therefore, when diffracted light of a light beam having a wavelength longer than the optimum wavelength enters the 3 rd surface 70c of the 2 nd diffraction element 70 via the 2 nd reflection unit 60, the diffracted light enters the 2 nd surface from a direction further rotated clockwise than the light beam having the optimum wavelength. Therefore, the light having the optimum wavelength and the light having a wavelength longer than the optimum wavelength are emitted in the same direction from the 2 nd diffraction element 70. This makes it difficult to reduce the resolution. Therefore, according to the present embodiment, wavelength compensation can be achieved, and image shift in the case where the wavelength of the image light L0 varies can be suppressed to be small.
The path of the image light L0 in the display module 10 of the present embodiment is as follows.
The image light L0 emitted from the image light generation device 20 is incident on the 1 st surface 50a of the 1 st diffraction element 50 via the condensing optical system 25. At this time, when a part of the image light L0 incident on the 1 st surface 50a of the 1 st diffraction element 50 is not diffracted, it passes through the 1 st diffraction element 50 as 0 th order diffracted light and is emitted from the 2 nd surface 50 b. The image light L0 emitted from the 2 nd surface 50b of the 1 st diffraction element 50 is reflected by the 1 st reflection unit 30 and then enters the 2 nd surface 50b of the 1 st diffraction element 50. The image light L0 incident on the 2 nd surface 50b of the 1 st diffraction element 50 is diffracted in a predetermined direction by the interference fringes and is emitted from the 2 nd surface 50b of the 1 st diffraction element 50. The image light L0 emitted from the 2 nd surface 50b of the 1 st diffraction element 50 is reflected by the 2 nd reflection unit 60, and then enters the 3 rd surface 70c of the 2 nd diffraction element 70. The image light L0 incident on the 3 rd surface 70c of the 2 nd diffraction element 70 is diffracted in a predetermined direction by the interference fringes and exits from the 3 rd surface 70c of the 2 nd diffraction element 70 to form an exit pupil G.
In other words, the 1 st diffractive element 50 transmits the image light L0 incident on the 1 st surface 50a from the image light generation device 20 via the condensing optical system 25 as 0 th order diffracted light, and emits the image light from the 2 nd surface 50b to the 1 st reflection unit 30. The 1 st reflection unit 30 reflects the image light L0 emitted from the 2 nd surface 50b of the 1 st diffraction element 50 toward the 2 nd surface 50b of the 1 st diffraction element 50. The 1 st diffraction element 50 diffracts the image light L0 incident on the 2 nd surface 50b from the 1 st reflection unit 30, and emits the image light from the 2 nd surface 50b to the 2 nd diffraction element 70. The 2 nd reflection unit 60 reflects the image light L0 diffracted by the 1 st diffraction element 50 toward the 2 nd diffraction element 70. The 2 nd diffraction element 70 diffracts the image light L0 incident on the 3 rd surface 70c from the 1 st diffraction element 50 and emits the image light from the 3 rd surface 70c to form an exit pupil G.
Therefore, when viewed from the normal direction of the virtual plane, a part of the optical path of the image light L0 emitted from the image light generating device 20 and transmitted through the 1 st diffraction element 50, a part of the optical path of the image light L0 reflected by the 1 st reflection part 30 and returned to the 1 st diffraction element 50, and a part of the optical path of the image light L0 diffracted by the 1 st diffraction element 50 and advanced to the 2 nd reflection part 60 overlap each other.
In general, a diffraction element is often used under the condition that 0 th order diffraction light is as small as possible and 1 st or more diffraction light is increased. In contrast, in the display module 10 of the present embodiment, since the 0 th order diffraction light transmitted through the 1 st diffraction element 50 is used as the image light L0, it is necessary to use the 0 th order diffraction light as much as possible. Here, the present inventors conceived that as a condition for securing the 0 th order diffracted light, the difference Δ n between the refractive index of the low refractive index portion 505 and the refractive index of the high refractive index portion 506 constituting the interference fringe 502 of the 1 st diffraction element 50 may be made relatively small.
The present inventors have conducted simulations relating to the transmittance when the refractive index difference Δ n is varied in order to obtain the optimum refractive index difference Δ n to secure the amount of 0 th order diffracted light.
Fig. 6 to 9 are graphs showing the relationship between the light use efficiency and the wavelength at a specific refractive index difference Δ n in the 1 st diffraction element 50. Fig. 6 is a graph when the refractive index difference Δ n is 0.035. Fig. 7 is a graph when the refractive index difference Δ n is 0.019. Fig. 8 is a graph when the refractive index difference Δ n is 0.010. Fig. 9 is a graph when the refractive index difference Δ n is 0.005.
In fig. 6 to 9, the horizontal axis represents the wavelength (nm) of light incident on the 1 st diffraction element. In the present simulation, green light having a wavelength of 532nm was assumed as light incident on the 1 st diffraction element. The vertical axis represents light use efficiency (%). The light use efficiency in fig. 6 to 9 indicates the ratio of the amount of light emitted from the 1 st diffraction element to the 2 nd reflection unit to the amount of light incident on the 1 st diffraction element, and is expressed by the product of the transmittance of 0 th order diffracted light with respect to the amount of light incident on the 1 st surface 50a of the 1 st diffraction element 50 and the reflectance of diffracted light with respect to the amount of light incident on the 2 nd surface 50b of the 1 st diffraction element 50. Therefore, for example, when the transmittance of the 0 th order diffracted light is 50% and the reflectance of the diffracted light is 50%, the light use efficiency in fig. 6 to 9 is 25%.
As shown in fig. 6, when the refractive index difference Δ n is 0.035, the light use efficiency tends to increase when the wavelength of the incident light is shifted from the designed value, that is, 532 nm. Specifically, when the wavelength of the incident light is shifted from 532nm by about ± 4nm, the light use efficiency can be obtained by about 5%. However, when the wavelength of the incident light is 532nm, which is a design value, the light use efficiency is about 0%. Therefore, the refractive index difference Δ n cannot be set to 0.035.
On the other hand, as shown in fig. 7, when the refractive index difference Δ n is 0.019, the light use efficiency tends to increase when the wavelength of incident light is shifted from 532nm, which is the design value, as in the case where the refractive index difference Δ n is 0.035. However, the light use efficiency when the refractive index difference Δ n is 0.019 is generally higher than that when the refractive index difference Δ n is 0.035. In the case where the wavelength of the incident light is 532nm, which is a design value, the light use efficiency is about 5%. Therefore, the refractive index difference Δ n of 0.019 can be used.
As shown in fig. 8, when the refractive index difference Δ n is 0.010, the light use efficiency varies when the wavelength of the incident light is shifted from 532nm, which is the design value, but the variation width is smaller than the refractive index difference Δ n is 0.035 or 0.019. The light use efficiency when the refractive index difference Δ n is 0.010 is higher than that when the refractive index difference Δ n is 0.019. In the case where the wavelength of the incident light is 532nm, which is a design value, the light use efficiency is about 8%. Therefore, it is preferable to use the refractive index difference Δ n of 0.010.
As shown in fig. 9, when the refractive index difference Δ n is 0.005, the fluctuation width of the light use efficiency due to wavelength fluctuation is smaller than when the refractive index difference Δ n is 0.010. The light utilization efficiency at 532nm of the designed wavelength of the incident light was about 5%. Therefore, the refractive index difference Δ n may be 0.005.
From the above simulation results, in order to ensure a predetermined light use efficiency in the 1 st diffraction element 50, the refractive index difference Δ n between the low refractive index portion 505 and the high refractive index portion 506 is preferably less than 0.020 and 0.005 or more. When the refractive index difference Δ n is 0.010, it is more preferable. By setting the refractive index difference Δ n as described above, the use efficiency of the image light L0 at the design center wavelength can be optimized. In the present simulation, the present inventors assumed that green light having a wavelength of 532nm was incident on the 1 st diffraction element 50, but it is predicted that substantially the same result can be obtained even when the light incident on the 1 st diffraction element 50 is other color light.
In the display device of patent document 1, the image light traveling from the image light generation device to the 1 st diffraction element and the image light traveling from the 1 st diffraction element to the mirror do not overlap each other. Therefore, the image light generation device must be disposed at a position away from the viewer's face, and the lateral width of the device increases, which may result in an increase in the size of the device.
In contrast, according to the display module 10 of the present embodiment, the optical paths of the image light L0 from the 1 st diffraction element 50 to the 2 nd reflection unit 60 are folded back 2 times when viewed from the normal direction of the virtual plane, and the optical paths overlap each other. Thus, according to the display module 10 of the present embodiment, the optical system can be reduced in size as compared with the display device of patent document 1.
In the display module 10 of the present embodiment, since the orientations of the 1 st diffraction element 50 and the 2 nd diffraction element 70 are appropriately arranged with respect to the incident direction of the image light L0, chromatic aberration generated by the 1 st diffraction element 50 and the 2 nd diffraction element 70 can be compensated for. As a result, the shift of the image when the wavelength is changed can be suppressed, and the resolution can be improved.
In addition, the display device 100 of the present embodiment includes the display module 10, and the display module 10 has the above-described effects, and thus is small in size and excellent in display quality.
[ 2 nd embodiment ]
Hereinafter, embodiment 2 of the present invention will be described with reference to fig. 10.
The basic configuration of the display module according to embodiment 2 is the same as that of embodiment 1, and the configuration of the 1 st diffraction element and the condensing optical system is different from that of embodiment 1. Therefore, the description of the entire display module is omitted.
Fig. 10 is a plan view showing a schematic configuration of a display module according to embodiment 2.
In fig. 10, the same components as those in fig. 2 used in embodiment 1 are denoted by the same reference numerals, and description thereof is omitted.
As shown in fig. 10, the display module 12 of the present embodiment includes an image light generating device 20, a condensing optical system 27, a 1 st diffraction element 55, a 1 st reflection unit 30, a 2 nd reflection unit 60, and a 2 nd diffraction element 70.
In the present embodiment, the 1 st diffraction element 55 includes: a 1 st surface 55a facing the condensing optical system 27; and a 2 nd surface 55b facing the 1 st reflecting part 30. The 1 st diffraction element 55 has a light transmission portion 55h, and the light transmission portion 55h transmits the image light L0 emitted from the image light generation device 20. The light transmitting portion 55h can be formed of, for example, a hole provided in the 1 st diffraction element 55. Alternatively, a region in which only a transparent member is present may be formed in a part of the 1 st diffraction element 55 without providing interference fringes, and the region may be a light-transmitting portion.
The condensing optical system 27 condenses the image light L0 emitted from the image light generation device 20 to the light transmission portion 55h of the 1 st diffraction element 55. Thus, substantially all of the light rays corresponding to the respective angles of view of the image light L0 emitted from the image light generating device 20 pass through the light transmitting portion 55h of the 1 st diffraction element 55. The condensing optical system 27 is constituted by one lens 271. However, the number of lenses 271 constituting the condensing optical system 27 is not particularly limited.
In the display module 12 of the present embodiment, the 1 st diffractive element 55 transmits the image light L0 emitted from the image light generating device 20 from the 1 st surface 55a to the 2 nd surface 55b through the light transmitting section 55h, and emits the image light L0 emitted from the 1 st reflective section 30 from the 2 nd surface 55b to the 2 nd diffractive element 70 through the 2 nd reflective section 60 in the portion other than the light transmitting section 55 h.
The other structure of the display module 12 is the same as that of the display module 10 of embodiment 1.
In this embodiment, the same effects as those of embodiment 1 can be obtained, which can provide a display module and a display device that are small and have excellent display quality.
The technical scope of the present invention is not limited to the above-described embodiments, and various modifications can be made without departing from the scope of the present invention.
For example, as described above, the 1 st diffractive element is not limited to the volume hologram element, and may be configured by, for example, a surface relief type diffractive element. However, when the 1 st diffraction element is a surface relief type diffraction element, in order to secure the amount of 0 th order diffracted light, it is preferable that the depth of the irregularities formed on the surface of the hologram element material be smaller than that of a general surface relief type diffraction element.
In the above-described embodiment, the structure in which the sum of the number of reflection times of the image light from the 1 st diffraction element to the 2 nd diffraction element and the number of generation times of the intermediate image is an even number is shown, but the sum of the number of reflection times of the image light from the 1 st diffraction element to the 2 nd diffraction element and the number of generation times of the intermediate image may be an odd number. For example, a 3 rd reflection unit may be provided between the 2 nd reflection unit and the 2 nd diffraction element, and the sum of the above may be 3 times. In this case, when viewed from the normal direction of the virtual plane, the 1 st direction with respect to the normal direction of the 1 st incident surface and the 2 nd direction with respect to the normal direction of the 2 nd incident surface may be located on different sides from each other. Therefore, for example, one of the 1 st direction with respect to the normal direction of the 1 st incident surface and the 2 nd direction with respect to the normal direction of the 2 nd incident surface may be located clockwise, and the other may be located counterclockwise.
Specifically, in the above-described embodiment, the sum of the number of times of reflection of the image light from the 1 st to 2 nd diffraction elements and the number of times of generation of the intermediate image is 2 or 3 times, but may be an even number other than 2. The sum may be 0 times, and 0 times is included in an even number. The sum may be an odd number other than 3.
The specific description of the shape, number, arrangement, material, and the like of each component of the display module and the display device is not limited to the above embodiments, and can be modified as appropriate.
The display module according to one embodiment of the present invention may have the following configuration.
(1) In the display module according to one aspect of the present invention, the display module may further include a 2 nd reflecting unit, and the 2 nd reflecting unit may reflect the image light diffracted by the 1 st diffractive element toward the 2 nd diffractive element.
(2) In the display module according to one aspect of the present invention, the 1 st diffractive element may transmit the image light emitted from the image light generating device as 0 th order diffracted light from the 1 st plane to the 2 nd plane, and may emit the image light emitted from the 1 st reflective portion as 1 st order diffracted light from the 2 nd plane to the 2 nd diffractive element.
(3) In the display module according to one aspect of the present invention, the 1 st diffraction element may be a volume hologram element having an interference fringe in which a low refractive index portion having a relatively low refractive index and a high refractive index portion having a relatively high refractive index are alternately provided, and a difference between the refractive index of the low refractive index portion and the refractive index of the high refractive index portion may be less than 0.020 and 0.005 or more.
(4) In the display module according to one aspect of the present invention, the 1 st diffractive element may have a light transmitting portion that transmits the image light emitted from the image light generating device, the 1 st diffractive element may transmit the image light emitted from the image light generating device through the light transmitting portion from the 1 st surface to the 2 nd surface, and the image light emitted from the 1 st reflective portion may be emitted from the 2 nd surface to the 2 nd diffractive element in a portion other than the light transmitting portion.
(5) In the display module according to one aspect of the present invention, the display module may further include a light condensing optical system that condenses the image light emitted from the image light generation device to the light transmission portion.
(6) In the display module according to one aspect of the present invention, when the image light is incident from the normal direction of the 2 nd surface, the 1 st diffraction element may diffract the image light with the highest diffraction efficiency in the 1 st direction, and when the image light is incident from the normal direction of the 3 rd surface, the 2 nd diffraction element may diffract the image light with the highest diffraction efficiency in the 2 nd direction, and the 1 st diffraction element and the 2 nd diffraction element may be arranged such that: when the sum of the number of reflections of the image light between the 1 st diffraction element and the 2 nd diffraction element and the number of generation of the intermediate image is an even number, the direction of the 1 st direction with respect to the normal direction of the 2 nd surface and the direction of the 2 nd direction with respect to the normal direction of the 3 rd surface are the same direction as each other when viewed from the normal direction of a virtual surface including the normal of the 2 nd surface and the normal of the 3 rd surface, and when the sum is an odd number, the direction of the 1 st direction with respect to the normal direction of the 2 nd surface and the direction of the 2 nd direction with respect to the normal direction of the 3 rd surface are different directions from each other when viewed from the normal direction of the virtual surface.
Claims (8)
1. A display module, having:
an image light generation device that generates image light;
a 1 st diffraction element having a 1 st surface and a 2 nd surface, which diffracts the image light;
a 1 st reflecting section that reflects the image light; and
a 2 nd diffraction element having a 3 rd surface for diffracting the image light,
the 1 st diffractive element transmits the image light incident on the 1 st surface from the image light generating device and emits the image light from the 2 nd surface to the 1 st reflective portion,
the 1 st reflecting unit reflects the image light emitted from the 1 st diffractive element toward the 2 nd surface of the 1 st diffractive element,
the 1 st diffraction element diffracts the image light incident on the 2 nd surface from the 1 st reflection unit and emits the image light from the 2 nd surface to the 2 nd diffraction element,
the 2 nd diffraction element diffracts the image light incident on the 3 rd surface from the 1 st diffraction element and emits the image light from the 3 rd surface to form an exit pupil.
2. The display module of claim 1,
the display module further includes a 2 nd reflection unit, and the 2 nd reflection unit reflects the image light diffracted by the 1 st diffraction element toward the 2 nd diffraction element.
3. The display module of claim 1 or 2,
the 1 st diffractive element transmits the image light emitted from the image light generating device as 0 th order diffracted light from the 1 st surface to the 2 nd surface, and emits the image light emitted from the 1 st reflective portion as 1 st order diffracted light from the 2 nd surface to the 2 nd diffractive element.
4. The display module of claim 3,
the 1 st diffraction element is constituted by a volume hologram element having interference fringes alternately provided with low refractive index portions having a relatively low refractive index and high refractive index portions having a relatively high refractive index,
the difference between the refractive index of the low refractive index portion and the refractive index of the high refractive index portion is less than 0.020 and 0.005 or more.
5. The display module of claim 1 or 2,
the 1 st diffraction element has a light transmitting portion that transmits the image light emitted from the image light generating device, and the 1 st diffraction element transmits the image light emitted from the image light generating device through the light transmitting portion from the 1 st surface to the 2 nd surface, and emits the image light emitted from the 1 st reflection portion from the 2 nd surface to the 2 nd diffraction element in a portion other than the light transmitting portion.
6. The display module of claim 5,
the display module further includes a light condensing optical system that condenses the image light emitted from the image light generating device to the light transmitting portion.
7. The display module of claim 1,
wherein the 1 st diffraction element diffracts the image light with the highest diffraction efficiency in the 1 st direction when the image light is incident from the normal direction of the 2 nd surface,
wherein the 2 nd diffraction element diffracts the image light with the highest diffraction efficiency in the 2 nd direction when the image light is incident from the normal direction of the 3 rd surface,
the 1 st and 2 nd diffractive elements are configured to:
when the sum of the number of reflections of the image light between the 1 st diffraction element and the 2 nd diffraction element and the number of generation of the intermediate image is an even number, when viewed from a normal direction of an imaginary plane including a normal line of the 2 nd surface and a normal line of the 3 rd surface, a direction of the 1 st direction with respect to the normal direction of the 2 nd surface and a direction of the 2 nd direction with respect to the normal direction of the 3 rd surface are the same direction as each other,
when the sum is an odd number, the direction of the 1 st direction with respect to the normal direction of the 2 nd surface and the direction of the 2 nd direction with respect to the normal direction of the 3 rd surface are different from each other when viewed from the normal direction of the virtual surface.
8. A display device, having:
a display module according to any one of claims 1 to 7; and
a housing that houses the display module.
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